1. Field of the Invention
The invention relates to fluidized catalytic cracking catalysts comprising in admixture a molecular sieve component, a large pore matrix component, and a rare earth component. Such catalysts exhibited improved performance in the presence of high levels of vanadium and/or nickel. This invention also relates to fluidized catalytic cracking (FCC) processes utilizing such catalysts.
FCC feed stocks can contain large quantities of metal contaminants including vanadium and nickel, which are the most deleterious. Accumulation of these metals can damage the FCC catalyst and adversely effect the product yield of the process. For instance, vanadium pentoxide formed in the regenerator causes irreversible destruction of the zeolite crystalline structure resulting in a loss of surface area and catalytic activity. Product selectivity will be altered significantly by the presence of vanadium causing the production of more undesired hydrogen and coke. Nickel which accumulates on the catalyst does not cause the destruction of crystalline zeolite material but does produce large quantities of hydrogen and coke.
It has therefore been deemed highly desirable to find a catalyst or process which reduces these negative effects of vanadium and nickel.
2. Prior Art
U.S. Pat. No. 4,341,661 issued to K. Barron et al. is believed relevant for its teaching that a bastnaesite component is effective in reducing the sulfur oxide and carbon monoxide emissions from an FCC regeneration zone. The bastnaesite may be employed in the form of separate particles which circulate through the FCC unit with the catalyst or the bastnaesite may be physically incorporated into the catalyst. Typical FCC catalyst components (matrix and binders) and preparation methods are disclosed. U.S. Pat. No. 4,429,053 issued to D. J. Ward describes a catalyst containing Y zeolites which are prepared by exchanging a sodium Y zeolite with one or more rare earth elements such as lanthanum and cerium. This reference states a mixture containing the rare earths in a distribution similar to that of the rare earth ore (e.g., bastnaesite, monazite, xenotime) is preferably used to introduce the recovered rare earth metals into the zeolite (column 5, lines 20-26). This catalyst is described as useful in a variety of reactions including hydrocracking, alkylation or cracking.
The catalytic deactivating effects of vanadium can be substantially prevented by incorporating a vanadium trapping agent. Alumina has been proposed as such a trapping agent (UK Patent Application GB 2,116,062A-1983) as have rare earth compounds (U.S. Pat. Nos. 4,515,683-1985). It is well known, however, that alumina addition results in a distinct deterioration in FCC catalyst selectivity, causing an increase in the undesirable yields of coke and light gases (YOUNG G. W., CREIGHTON J., WEAR C. C., and RITTER R. E. Paper AM-87-51 presented at the 1987 NPRA Annual Meeting March 1987, San Antonio, Tex.).
Large pore (&gt;90 angstrom avg. diameter) matrices have been claimed to be more suitable than small pore matrices in that the large pore matrices reduce the coke and light gas formation caused by the contaminant metals (U.S. Pat. Nos. 3,944,482-1976), the teachings of which are incorporated herein by reference. Moreover, it has been maintained that the best performance is obtained with a matrix that contains a high level of this large pore component, specifically greater than 25 wt % of the matrix and preferably more than 50 wt % of the matrix.
U.S. Pat. No. 4,515,683 teaches that rare earth impregnation on the catalyst works better as a metals trap than does ion exchanged rare earth. In addition a high degree of rare earth prevents the FCC catalyst from acting as an octane catalyst. (Upson L. L.--"What to look for in Octane Catalyst"--Paper given at Katalistiks Octane Symposium, Amsterdam, January 1986).
U.S. Pat. No. 4,606,813 issued to J. W. Byrne et al. is directed to an FCC catalyst comprising a blend of a catalytically active first component and a second component for reducing sulfur oxide emissions from the FCC regenerator. The second component comprises at least 70 wt. % alumina having an equilibrium surface area of 40-100 m.sup.2 /g.